The invention relates to a variable track wheel of the type comprising a rim and a disc mounted together in a removable manner.
Variable track wheels comprising a rim are known, on which the tire is mounted, having a cylindrical base on the internal circumferential surface of which there is provided a connecting member that projects radially towards the rotation axis of the wheel. A disc is removably secured to the connecting member, the wheel being fitted to a hub by means of the disc. The connecting member comprises a circumferentially continuous single annular element or a plurality of circumferentially equidistant lobes.
The disc is secured to the connecting member by fastenings, such as fixing bolts, passing through connecting holes provided in both disc and connecting member.
As the disc has a concave face and a corresponding convex fact, by varying the axial mounting position between the rim and disc, or by rotating the disc around the vertical diameter thereof, the distance varies between the median plane of the rim and the plane of the hub against which the disc is mounted, this causing a pair of wheels on the same axle to be brought nearer or moved further away. Such wheels are, for example, used as wheels of agricultural machines, such as tractors, in which, to comply with different agricultural applications, the rim and the disc must be able to be assembled according to alternative axial positions or orientations.
One drawback of variable track wheels of known type is that as they are wheels of relatively large dimensions, it is rather difficult to assemble the disc and the rim in such a manner that the respective rotation axes are effectively coaxial. In fact, gravity and the play between the fixing bolts and the connecting holes provided on both disc and connecting member, to ensure assembly thereof, cause the axis of the disc, once mounted, not to be aligned on the axis of the rim. This axial misalignment between rim and disc has a negative effect on the stroke and performance features of the vehicle on which the wheel is mounted. In particular, the misalignment causes vibrations that are transmitted to the vehicle, with the risk of causing the driver problems of comfort or even problems of safety due to instability of the vehicle.
This is particularly relevant to vehicles that are arranged for travelling at relatively high speeds, for example even at 50 kilometers an hour.
Variable track wheels are known in which the misalignment of the axes of the disc and of the rim has been considered.
EP0808250 discloses a variable track wheel in which the disc is provided with additional holes that during mounting are aligned on at least two indicators or holes provided on the rim and reciprocally coupled by centering plugs that can be removed once the fixing bolts have been tightened.
EP0911183 discloses a variable track wheel wherein the disc is provided with a pair of diametrically opposite centering pins, arranged for coupling with a plurality of pairs of corresponding diametrically opposite holes obtained on the connecting member.
The centering systems of known type are not designed for repeating centering during mounting of the disc and of the rim after first mounting.
In fact, during removal of the centering pins or during subsequent inserting of the pins into the corresponding holes, the walls of the holes into which the centering pins have to be inserted for centering can become damaged, this causing possible play that reduces the precision of the subsequent mounting.
Still another drawback of known systems is that in the event of replacement of only the rim or only the disc with a new rim or a new disc, the new rim or the new disc has to be provided with holes or pins having dimensions that are compatible with those found on the piece with which they have to be coupled. This means that a large number of spare parts have to be kept in store so that one disc model can be mounted on a plurality of models of rim and vice versa the same centering system can be maintained.
Alternatively, to mount, for example, a new disc on an old rim, it is necessary to work on the old rim or on the new disc, for example, to match the dimensions of the holes with those of the pins, this increasing significantly the time and cost of replacement. Lastly, the centering systems of known type are not effective on all the types of variable track wheel, in particular on wheels comprising spacers between the disc and connecting member.
One object of the invention is to improve the centering systems of known type to limit the misalignment of the axes of the disc and of the rim of a wheel. A further object is to obtain a variable track wheel in which the disc and the rim can be replaced individually with spare parts, without it being necessary to perform mechanical machining to adapt the centering system of the spare part with that of the disc and/or of the rim that has not been replaced.
Still another object is to provide a centering system that can be applied to a variable track wheel comprising spacers between the disc and connecting member. Another object is to obtain a variable track wheel in which the mounting position between disc and rim ensures a set balance of the wheel.
A still further object is to produce a variable track wheel, in which the mounting position between disc and rim corresponding to a set balance of the wheel can be refound with a certain precision at each reassembly of the disc of the rim following the first mounting during manufacture.
According to the invention, a variable track wheel is provided comprising a rim that is suitable for receiving a tire, and a disc through which said wheel is mountable on a hub, said disc being removeably secured by fastenings to a connecting member provided in said rim, said connecting member projecting towards a rotation axis of said wheel, said wheel further comprising a plurality of spacers interposed between an annular perimeter zone of said disc and said connecting member of said rim, said disc and said rim being mountable in a plurality of reciprocal axial positions and in a plurality of reciprocal orientations to obtain a variation in the track of said wheel, said wheel further comprising at least one centering device for mutual positioning of said disc and of said rim, said centering device comprising a hole and a pin, said hole or said pin being provided in said connecting member or in said disc, characterized in that said centering device further comprises a coupling element shaped in such a manner as to cooperate with said hole and with said pin for mutually coupling said pin and said hole.
Owing to the coupling element, the diameter of the hole/pin provided on the connecting member can also be substantially different from the diameter of the pin/hole provided on the disc, inasmuch as it is the coupling element that adapts the dimensions of the hole to those of the pin.
In one embodiment, the wheel comprises two centering devices, each of which is provided with a corresponding coupling element.
In a further embodiment, the two centering devices are diametrically opposite and are dimensionally different from one another, i.e. the pin, the hole and the coupling element of the first centering device have dimensions—in particular the diameter—other than those of the respective pin, hole and coupling element of the second centering device.
This enables the mounting position of the rim and of the disc to be found unequivocally, whatever the mutual axial position or orientation of the rim and disc, and enables a set balance of the wheel to be obtained.
As the wheel comprises spacers that are interposed between said connecting member and said disc and retained between said connecting member and said disc by the fastenings, in particular by bolts, the coupling element, in addition to coupling the pin with the hole, compensates the distance imposed by the spacers between the disc and the connecting member.